The present invention relates generally to an article having interrupted threads and a mold for manufacturing the same. More specifically, the present invention relates to a mold apparatus which is capable of manufacturing an article having a female threaded aperture for receiving male threaded members.
In the field of threaded articles, namely, articles with female threaded apertures for receiving male threaded members, it has been well known that such an article can be created by first molding the article leaving an aperture completely therethrough. Next, to create the female threads on the inner wall of the aperture through the article, it has been well known to unscrew a mandrel through the aperture, preferably when the molded article is still soft, to create the internal female threads by tooling. This well-known process requires the multiple steps of molding the piece and then unscrewing a mandrel to form a continuous female thread on the inner wall of an aperture through the article. This is the only known process for creating internal female threads where an aperture extends completely through an article. For example, nuts and screw hole apertures are formed in this fashion.
To avoid the use of a mandrel and a separate tooling step for creating threads, it has been well known to employ a collapsible core which includes a set of fingers with thread matrices thereon to form a thread pattern in the molding process. Each of these collapsible core-type molding devices, due to their construction, only have application in forming internal threads on various types of closures, such as plastic bottle caps, and the like. These molded articles do not have apertures positioned completely therethrough.
For example, U.S. Pat. No. 4,938,679, issued to Pietrorazio, incorporated herein by reference, discloses a collapsible core for molding closures having interrupted interior threads. In particular, this patent teaches the employment of a collapsible core with a number of fingers having thread matrices thereon which spread apart during the molding process and then collapse to permit removal of the completed molded bottle cap. The resultant thread pattern is a number of groups, depending on the number of collapsible fingers, of multiple thread segments vertically aligned with one another. Large gaps remain between each of the groups to permit the fingers to collapse during the removal process. In addition, U.S. Pat. No. 3,618,170, issued to Owens, incorporated herein by reference, discloses an apparatus for molding plastic closures which includes a pair of collapsible fingers for forming two groups of internal threads within the closure article. Large smooth portions remain on the inner wall between the two groups of thread segments. In each of the foregoing collapsible core-type molding apparatuses, a large number of moving parts are required to enable the collapsible core to open and close. Such apparatuses experience severe wear since they repeatedly open and close for each molded cap produced.
The foregoing known prior art apparatuses and methods for producing internal threads have serious drawbacks in certain applications. In particular, referring first to the method of unscrewing a mandrel through an aperture to create the threads by tooling, only certain plastics are capable of being manipulated in this manner to create threads. There are certain high temperature and heat-resistant plastics which are not well suited for injection molding and, in particular, being subject to mandrel tooling for the creation of threads in an aperture. In addition, a quality thread engagement is critical in certain applications and environments such as high heat situations. As a result, the groups of threads created by the collapsible core-type devices are unacceptable for creating threads for use in high temperature environments due to the large gaps present between each of the groups. High temperatures will cause the article material to buckle, thus requiring better thread coverage about the periphery of the threaded aperture.
As a result of the disadvantages found in the prior art devices, there is a demand for the ability to create internal threads on an aperture wall of an article made of any material required by the manufacturer. It is also desirable to manufacture a threaded article which is less susceptible to defects due to wear and requires a mold apparatus which has few moving parts and is easy to maintain.